Data Deficient birds on the IUCN Red List: What don’t we know and why does it matter?

Abstract

Species are classified as Data Deficient on the IUCN Red List if there is inadequate information to make an assessment of their extinction risk based on distribution and/or population status. Data Deficient is probably the most controversial and misunderstood of IUCN Red List categories. All 63 globally Data Deficient bird species lack sufficient information on population size, trends, distribution and/or threats to assess them against the Red List criteria. For 10 species (16%) the paucity of data may be a consequence of taxonomic uncertainty. Three species are known only from specimens of uncertain geographic provenance. Since 1988, 58 Data Deficient birds have been recategorised, mainly as Near Threatened (48%) or Least Concern (16%). We speculate that of the remaining Data Deficient birds, just 14% may prove to be threatened. Proportionately fewer birds (0.6%) are listed as Data Deficient as compared with mammals (15%), amphibians (25%), corals (17%), conifers (4%) and cycads (6%), because birds are better known and perhaps because for birds greater use is made of contextual information (e.g. condition of habitats, likely ecology/habitat preferences and trends in known threatening processes) to assign alternative categories where this is plausible and precautionary. Ensuring consistency between taxonomic groups is essential for the credibility of the IUCN Red List. For non-avian taxa, the higher proportions of Data Deficient species introduces greater uncertainty in estimates of overall extinction risk, but the results from birds hint that the real values may fall at the lower end of these estimates. Data Deficient species should be treated precautionarily in terms of protection and assessing environmental impacts, and regarded as urgent priorities for surveys and research to elucidate their true status. Greater attention should also be given to documenting data quality and uncertainty for Red List assessments of threatened and non-threatened species.